I assume you are having this issue with Writer and Calc? There are three levels at which file-locking activity can be engaged: operating system, application, and record (as with databases). Reviewing the LibreOffice documentation, it appears that Writer and Calc have collaboration tools where you can manually engage locking protocols. My guess, however, as a single user, there is no collaboration going on here and even if these protocols were engaged, I doubt they would remain in permanent lock. So that narrows down to the operating system.
I would suggest closing all LibreOffice activity, and attempt to open the file in question using an alternative application, such as WordPad. If it complains, it is likely an O/S level lock of some sort. If it works, close the file and attempt to reopen it in LibreOffice.
Another tell-tale sign of a problem is a lingering lock file from a previous operation. For example,
~lock.Linux Daily Operations Guide.docx#
These lock files will reside in the same folder as the document you are attempting to open. MS Word has issues with this from time-to-time as well. Suggest you back this file up and then delete it, then attempt to reopen the document in question.